Physiological and physico-chemical properties of blood

The density and viscosity of the blood

The density of human blood (and pets) is 1,050-1,060, for an average of 1,057 men, women – 1,053. It depends mainly on the number of red blood cells or hemoglobin contained in them, and to a lesser extent – the composition of the liquid portion of the blood; increases water loss after, for example after sweating. When blood loss density decreases.
The viscosity of the blood due to internal friction at moving some of its particles relative to others. In determining the blood viscosity is the viscosity of the water unit.

Viscosity human whole blood under physiological conditions varies from 4 to 5 and the viscosity of blood plasma – from 1.5 to 2. The viscosity of whole blood depends mainly on the number of red blood cells and their volume and to a lesser extent – the composition of the plasma (preferably quantities of proteins present in it and to a lesser extent – on the content of salts).
Due to the swelling of venous blood viscosity erythrocyte viscosity greater arterial blood. Continuous operation of medium gravity lowers blood viscosity and improves its hard work.

The salt composition, osmotic and colloid osmotic (oncotic) blood pressure

Mineral salts plasma is about 0.9-1%. The amounts of the salts in the plasma are relatively stable under normal conditions fluctuate within a small range. Different species mineral content in the blood plasma varies.
The physiological significance of blood electrolytes is that they: 1) maintain the relative constancy of the osmotic pressure of the blood; 2) maintain the relative constancy of the active reaction of the blood; 3) effect on metabolism and 4) influence the state of colloids.

The relative constancy of the osmotic pressure of the blood is of great biological importance as a condition for maintaining relatively constant osmotic pressure in the tissues. Sharp fluctuations in osmotic pressure in the tissues lead to violations of their activities, and even to their death. The constancy of the osmotic pressure of the blood retains the integrity of red blood cells.
Under normal conditions, the osmotic pressure of the erythrocyte, plasma and blood cells in tissues and organs of human and mammals equals 778 316 – 818 748 Pascals.

Despite the high protein content, the number of protein molecules in plasma is low because of their large molecular weight. Therefore, they create colloidal osmotic (oncotic) pressure is equal in all plasma 3325 – 3990 Pa and the osmotic pressure of blood plasma maintained at a predetermined, relatively constant mainly minerals.

Among minerals major role in maintaining the osmotic pressure member salt – sodium chloride. The magnitude of the osmotic pressure is determined by the depression of the freezing point depression method, the freezing point or lowering blood below 0 °. Rates of depression indicated Δ (delta). In humans, blood is Δ 0,56 ° (0,56-0,58 °), hence the molecular concentration in plasma is approximately 0.3 g-moles per 1 dm3.

The reaction of the blood

The active reaction of the blood, like that of any solution depends on the concentration of hydrogen (H +) and hydroxyl (OH-) ions. The average pH of human blood, horses and dogs at 37 ° C was 7.35. Thus, the reaction of the blood weakly alkaline.
Change in body temperature does not affect the pH of the blood, which is stored with significantly more constant than the body temperature. This constancy of the pH is provided by the excretory organs, as well as the composition of red blood cells and blood plasma. The fact that the composition of plasma is essential to maintain a constant pH, is proved by the fact that the reaction to shift to the alkaline side to the plasma need to add about 70 times more sodium hydroxide than to clean water, as well as to shift the reaction to the acid side you need to add more than 3.25 times more hydrochloric acid than water (see. as the article “Chemical Reactions”). Persistence depends on the reaction of the blood buffer systems.


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Physiological and physico-chemical properties of blood